A Yellow Leaf Scorpionfish (Taenianotus triacanthus) perched amongst a set of hard corals on the coral wall at the famous Steve's Bommie dive site in the Great Barrier Reef in Queensland, Australia.
These distinctive Scorpionfish have a compressed head and body with a large fan like dorsal fin - thus its comparison to a Leaf. They are often referred to as Leaffish.
Leaf Scorpionfish come in a variety of colors, normally mimicking their surroundings as they are ambush predators. Also in general these fish are found in pairs, so if one is spotted - which is not easy - it is well worth looking for a second fish nearby.